1. Field of the Invention
The present invention relates to novel aqueous acid cleaning compositions thickened by an effective amount of a polysaccharide, and to the use of such compositions for the cleaning of stained, soiled or fouled surfaces.
2. Description of the Prior Art
It is conventional in this art to use aqueous acid compositions to remove inorganic and organic deposits adhering to a variety of surfaces. These inorganic deposits typically include compounds such as carbonates, sulfates or oxides of metals, such as of calcium, magnesium, potassium and iron. Compositions based on hydrochloric acid or formic acid are customarily used to remove tartar from porcelain surfaces and compositions containing phosphoric acid are well known for the elimination of rust from metal surfaces. Advantageously, liquid cleaning compositions are thickened by means of a viscosifying agent such that the product may be applied to surfaces that are inclined or irregular in shape without excessive running, in order to provide a sufficient contact time between the acid and the surface to be cleaned.
The use of a thickener displaying Newtonian behavior in aqueous solution is not satisfactory, as the solution always has a tendency to flow, even if the thickener is incorporated in relatively large amounts. Cleaning compositions of a non-Newtonian character comprising a thickener such as xanthan gum, have already been proposed to this art; see, for example U.S. Pat. No. 3,578,499 and published European application No. 0,091,194. Although xanthan gum is considered to be reasonably stable at low pH values, it nevertheless hydrolyzes in the presence of an acid, giving rise to a reduction in viscosity and of the flow threshold. These compositions, therefore, cannot be stored for extended periods of time without losing their rheological properties.
In U.S. Pat. No. 4,302,253 certain cleaning compositions are proposed which include a solution of a mineral acid thickened with a clay, xanthan gum and an imidazoline. The imidazoline serves as the anti-flocculating agent for the clay. These compositions are stable for several months, but they have the disadvantage of a relatively high cost.
In actual practice, serious need has long existed for low cost aqueous acid compositions having all of the viscosity desired, a high flow threshold and the necessary stability in storage.